using Silk.NET.Input;
using Silk.NET.OpenGL;
using Silk.NET.OpenGL.Extensions.ImGui;
using Silk.NET.Windowing;

namespace AcDream.UI.ImGui;

/// <summary>
/// Owns the <c>ImGuiController</c> from <c>Silk.NET.OpenGL.Extensions.ImGui</c>,
/// which handles the whole Silk.NET ↔ ImGui.NET integration:
/// <list type="bullet">
///   <item>Creates the ImGui context + OpenGL3 backend using Silk.NET's GL binding
///     (no GLFW / SDL dependency — unlike Hexa.NET.ImGui, which assumed one).</item>
///   <item>Subscribes to Silk.NET's window + input events to drive IO.</item>
///   <item>Per frame: <c>Update(dt)</c> calls <c>ImGui.NewFrame()</c>; <c>Render()</c>
///     calls <c>ImGui.Render()</c> + uploads draw data via its OpenGL3 backend.</item>
/// </list>
///
/// <para>
/// Instance-scoped rather than static so GL-context lifetime is explicit.
/// <c>GameWindow</c> owns the one instance and disposes on shutdown.
/// </para>
///
/// <para>
/// History: tried <c>Hexa.NET.ImGui</c> + <c>Hexa.NET.ImGui.Backends.OpenGL3</c> first
/// per the original plan, but its native OpenGL3 backend resolves GL functions
/// via GLFW / SDL internally and crashed (0xC0000005) in <c>InitNative</c> without
/// one of those present. Pivoted to the official Silk.NET extension on 2026-04-25.
/// </para>
/// </summary>
public sealed class ImGuiBootstrapper : IDisposable
{
    private readonly ImGuiController _controller;

    public ImGuiBootstrapper(GL gl, IView window, IInputContext input)
    {
        ArgumentNullException.ThrowIfNull(gl);
        ArgumentNullException.ThrowIfNull(window);
        ArgumentNullException.ThrowIfNull(input);
        // ImGuiController constructor handles:
        //   - ImGui.CreateContext()
        //   - ImGuiOpenGL3 shader + vertex-buffer init (via Silk.NET GL)
        //   - Keyboard + mouse event subscription (bound to Silk.NET IInputContext)
        //   - Default style = dark
        _controller = new ImGuiController(gl, window, input);
    }

    /// <summary>
    /// Begin an ImGui frame. Call BEFORE any <c>ImGui.*</c> widget calls.
    /// Internally: consumes buffered input events, calls <c>ImGui.NewFrame()</c>.
    /// </summary>
    public void BeginFrame(float deltaSeconds) => _controller.Update(deltaSeconds);

    /// <summary>
    /// Finalise the ImGui frame and draw to the framebuffer. Call AFTER all
    /// panel draws, within the same frame as <see cref="BeginFrame"/>. The
    /// OpenGL3 backend save/restores the GL state it touches (shader, VAO,
    /// texture, blend, scissor); state not in its save-list (e.g.
    /// <c>GL_FRAMEBUFFER_SRGB</c>) is caller's responsibility.
    /// </summary>
    public void Render() => _controller.Render();

    public void Dispose() => _controller.Dispose();
}